Utilization of geothermal energy

ABSTRACT

Fluid is introduced to one or more underground fluid passages in thermal contact with a hot rock formation. Kinetic energy of the fluid being introduced is converted into electrical energy. The introduced fluid absorbs heat from the hot rock formation. That absorbed heat is extracted from the heated fluid for use in connection with a domestic or industrial application.

FIELD OF THE INVENTION

This disclosure relates to utilization of geothermal energy and, more particularly, relates to systems and methods for efficiently extracting geothermal energy from an underground hot rock formation.

BACKGROUND

High-temperature, underground rock formations are found in numerous locations throughout the world. Such formations store large amounts of energy in the form of heat. When ground water percolates down into such formations, the water is heated and may flow to the earth's surface as geysers or hot springs. When such formations are dry, heat may be recovered from them by pumping water down to the formation and heating the water by contact with the formation.

SUMMARY OF THE INVENTION

In one aspect, a method includes introducing fluid to one or more underground fluid passages in thermal contact with a hot rock formation, converting kinetic energy of the fluid being introduced to the one or more underground fluid passages into electrical energy, absorbing heat from the hot rock formation into the introduced fluid and extracting the absorbed heat from the heated fluid for use in connection with a domestic or industrial application. In a typical implementation, the hot rock formation is an underground hot dry rock formation.

In some implementations, converting the kinetic energy of the fluid being introduced includes directing the fluid through a turbine-generator. The fluid typically flows through the turbine-generator at least partially under the influence of gravity and, in some implementations, it flows entirely under the influence of gravity. The turbine-generator typically is positioned as near as possible to the hot rock formation without undue risk that static fluid may accumulate above the hot rock formation to a level that will unduly impede fluid flow through the turbine-generator.

In some implementations, prior to extracting the absorbed heat from the heated fluid, the heated fluid is removed from thermal contact with the hot rock formation. This may be done with a pump or by virtue of the fluid naturally flowing upward as a vapor.

In certain embodiments, the fluid is introduced through a fluid injection well that extends from the earth's surface to contact the hot rock formation and the fluid is removed through a fluid production well that also extends from the earth's surface to contact the hot dry rock formation.

The one or more underground passages may include a horizontal borehole in the hot rock formation that extends between the fluid injection well and the fluid production well. Alternatively, the one or more underground passages may include fractures formed in the hot rock that extend between the wells.

Heat may be extracted from the heated fluid for use in connection with a domestic or industrial application by a heat exchanger located above the hot rock formation. The extracted heat may be used in connection with a domestic or industrial application, such as to run a turbine-generator, to heat a home or building, to provide a heat source for an industrial application. After extracting the absorbed heat from the heated fluid, the method typically includes returning the fluid to be reintroduced to the one or more underground fluid passages.

In another aspect, a system includes an underground hot rock formation, a fluid injection well that facilitates introducing fluid to one or more underground fluid passages in thermal contact with the underground hot rock formation and a turbine-generator arranged to convert kinetic energy of the fluid being introduced into electrical energy/ The system is arranged so that introduced fluid absorbs heat from the hot rock formation. The system also is arranged so that the absorbed heat is extracted for use in connection with a domestic or industrial application. The hot rock formation typically is an underground hot dry rock formation.

In some implementations, the system is arranged so that fluid introduction occurs at least partially under the influence of gravity or entirely under the influence of gravity. The turbine-generator typically is positioned as near as possible to the hot rock formation without being so low that an undue risk exists that static fluid may accumulate above the hot rock formation to a level that will unduly impede fluid flow through the turbine-generator.

Typically, a fluid production well facilitates removing heated fluid from the one or more underground passages. A pump may be provided beneath a static fluid level in the fluid production well to remove fluid from thermal contact with the hot rock formation. Alternatively, the heated fluid may be a vapor that is removed from thermal contact with the hot rock formation by naturally flowing upward through the fluid production well as a vapor.

In certain embodiments, the underground passage(s) include a horizontal borehole in the hot rock formation. In such instances, the horizontal borehole extends between the fluid injection well and a fluid production well. The underground passage(s) also may include fractures formed in the hot rock formation.

A heat exchanger may be provided to extract absorbed heat from heated fluid for use in connection with a domestic or industrial application. In some implementations, a pipe extends from the heat exchanger to the fluid injection well to return fluid, after the absorbed heat is extracted, to be reintroduced to the one or more underground fluid passages.

In yet another aspect, a system includes an underground hot rock formation having one or more surfaces that define one or more underground fluid passages in thermal contact with a hot dry rock formation. A fluid injection well is arranged to facilitate introducing fluid to the one or more underground fluid passages. The introduced fluid can absorb heat from the hot rock formation. A fluid production well is arranged to facilitate removing fluid from the one or more underground fluid passages. A turbine-generator is arranged relative to the fluid introduction well so as to convert kinetic energy of the fluid being introduced into electrical energy. A heat exchanger is provided to extract the absorbed heat for use in connection with a domestic or industrial application.

In some implementations, one or more of the following advantages are present.

For example, a large amount of geothermal energy may be drawn from underground hot rock formations in a highly efficient manner. Such energy may be harnessed in an environmentally friendly manner as well.

Other features and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional elevation view of a geothermal energy system.

FIG. 2 is a cross-sectional elevation view of another geothermal energy system.

FIG. 3 is a cross-sectional elevation view of yet another geothermal energy system.

FIG. 4 is a cross-sectional elevation view of still another geothermal energy system.

FIG. 5 is a cross-sectional elevation view of another geothermal energy system.

FIG. 6 is a cross-sectional elevation view of another geothermal energy system.

DETAILED DESCRIPTION OF THE DRAWINGS

The system 100 of FIG. 1 is adapted to draw thermal energy from an underground hot rock formation in a cost-efficient manner.

The illustrated system 100 includes an underground hot dry rock formation 102, a fluid injection well 104 and a fluid production well 106. The illustrated hot dry rock formation 102 is a subsurface rock structure that is heated by geothermal energy. One or more passages (not visible in FIG. 1) extend through and/or near the hot dry rock formation 102. These passages are in thermal contact with the hot dry rock formation 102 so that fluid carried therein is able to absorb heat from the hot dry rock formation 102.

The fluid injection well 104 extends from the earth's surface 114 to the hot dry rock formation 102. In the illustrated system, the fluid injection well 104 provides a channel through which fluids can be introduced to the passages through and/or near the hot dry rock formation 102. The fluid production well 106 also extends from the earth's surface 114 to the hot dry rock formation 102. In the illustrated system, the fluid production well 106 provides a channel through which fluid can be removed from the passages that extend through and/or near the hot dry rock formation.

A turbine-generator 108 is in the fluid injection well 104 and arranged to convert kinetic energy of fluid flowing downward through the fluid injection well 104 into electrical energy. Typically, such fluid flows at least partially under the influence of gravity and, in some implementations, flows entirely under the influence of gravity. The fluid injection well 104 should be sufficiently large and the passage(s) in the hot dry rock formation should have sufficient fluid carrying capacity to accommodate a substantially steady flow of fluid, under the influence of (or at least substantially under the influence of) gravity, through the fluid injection well 104.

It is generally desirable that the turbine-generator 108 be located as low as practical in the fluid injection well 104 so that the fluid flowing through the turbine-generator 108 will have fallen a great distance and, therefore, gained a large amount of kinetic energy. The turbine-generator 108 should not, however, be so low in the fluid injection well 104 that an undue risk exists that static fluid may accumulate in the bottom of the fluid injection well 104 to a level that would unduly impede fluid flow through the turbine-generator 108. For example, if it is expected that under certain operating conditions, static fluid might accumulate in the fluid injection well 104 to a certain level, it is desirable that the turbine-generator 108 be located above that level so that the turbine-generator 108 does not become submerged in substantially static fluid during system operation.

Determining the turbine-generator's ideal height in the fluid injection well 104, therefore, may involve considering, among other things, the ability of the passages in and/or near the hot dry rock formation 102 to absorb fluid, the size of the fluid injection well 104, the size of the fluid production well 106 and how far below the earth's surface the hot dry rock formation 102 is located.

A pump 110 is located in the fluid production well 106 and arranged to remove fluid from fluid production well 106 and the passages that extend through and/or near the hot dry rock formation 102. It is generally desirable that the pump be located lower than the expected static fluid level in the fluid production well 106.

A heat exchanger 112 is arranged to extract heat from heated fluid that comes out of the production well 106 for use in connection with a domestic or industrial application. The illustrated heat exchanger is above the earth's surface 114 and includes a primary fluid circuit 116 and a secondary fluid circuit 118. The illustrated heat exchanger 112 is arranged so that fluid from the dry rock formation 102 flows through the primary fluid circuit 116 and a working fluid to be heated flows through the secondary fluid circuit 118. The primary 116 and secondary 118 fluid circuits are thermally coupled to one another so that heat from fluid flowing in the primary fluid circuit 116 can transfer to fluid flowing in the secondary fluid circuit 118.

A first set of pipes 120, 122 extends between the heat exchanger's 112 primary fluid circuit 116 and the fluid injection and fluid production wells 104, 106, respectively. A second set of pipes 124, 126 extends from the heat exchanger's 112 secondary fluid circuit 118 to an external device or devices (not illustrated).

During system 100 operation, fluid is introduced to the fluid passage(s) that are in thermal contact with the hot dry rock formation 102 through fluid injection well 104. Fluid flows downward in the fluid injection well 104 at least partially (if not entirely) under the influence of gravity. That fluid flows through the turbine-generator 108. The turbine-generator 108 converts the flowing fluid's kinetic energy into electrical energy. This electrical energy is delivered to an electrical power system (not illustrated in FIG. 1) for use in connection with a domestic or industrial application.

Fluid then flows from the fluid injection well 104 to the fluid production well 106 through one or more passages (e.g., fractures in the hot dry rock formation 102 that are not illustrated in FIG. 1) in and/or near the hot dry rock formation 102, absorbing heat from the hot dry rock formation 102 along the way. The amount of heat that the fluid absorbs depends, inter alia, on the temperature of the hot dry rock formation 102, the distance between wells 104, 106, the physical configuration of the passages that extend between wells and the rate of fluid flow through the passages. Once the fluid has been heated, pump 110 pumps the heated fluid upward and out of the fluid production well 106.

The heated fluid then flows through pipe 122 into the heat exchanger 112, which extracts heat from the heated fluid for use in connection with a domestic or industrial application. More particularly, the heated fluid enters the heat exchanger's primary fluid circuit 116. Working fluid is provided to the heat exchanger's 112 secondary fluid circuit 118 via pipe 124 and is removed from the heat exchanger's 112 secondary fluid circuit 118 via pipe 126. The working fluid in the heat exchanger 112 is heated by hot fluid in the primary fluid circuit 116 and may be, for example, flashed to steam (or other vapor) which is used to turn a turbine-generator to generate electric power. In general, heat that is extracted from the heated fluid is used in connection with some industrial or domestic application.

Once heat is extracted, fluid returns to the fluid introduction well 104 via pipe 120. Make-up fluid may be added to the system 100, for example, at a point on pipe 120 (not shown) in order to replace water lost by leakage.

The system 200 of FIG. 2 is similar to the system 100 of FIG. 1 except that, the system 200 of FIG. 2 includes a horizontal borehole 228 formed in the hot dry rock formation 102.

The horizontal borehole 228 extends between the fluid injection well 104 and the fluid production well 106. The horizontal borehole 228 may be formed, for example, by using conventional horizontal drilling techniques.

Operation of the system 200 in FIG. 2 is similar to operation of the system of FIG. 1 except that, during operation of the system of FIG. 2, fluid flows from the fluid injection well 104 to the fluid production well 106 through the horizontal borehole 228 in the hot dry rock formation 102, absorbing heat from the hot dry rock formation 102 along the way.

The system 300 of FIG. 3 is similar to the system 200 of FIG. 2 except that, the system 300 of FIG. 3 does not include a pump (e.g., pump 110 in FIG. 2) in the fluid production well. In the illustrated implementation, such a pump is not necessary because the system 300 is arranged so that the fluid absorbs sufficient heat by the time it reaches the fluid production well 106 that the heated fluid rises in and exits the fluid production well 106 as a vapor (e.g., steam). Typically, the vapor condenses in the heat exchanger 112 as it gives up heat to the working fluid in the secondary fluid circuit 118. Once heat is extracted, the substantially condensed fluid returns to the fluid introduction well 104 via pipe 120.

In general, whether a pump (e.g., pump 110 in the system 100 of FIG. 1) is required in a fluid production well 106, depends on the phase (liquid or vapor) of the fluid in the fluid production well 106. If, during system operation, fluid exists in the fluid production well 106 substantially as a vapor, then such a pump may not be necessary. If on the other hand, during operation, fluid exists in the fluid production well 106 substantially as a liquid, then such a pump may be necessary or at least desirable.

Whether the fluid in the fluid production well 106 is substantially liquid or substantially vapor may depend, inter alia, on the temperature of the hot dry rock formation 102, the distance between wells 104, 106, the physical configuration of the passages that extend between wells, the rate of fluid flow through the passages, the depth of the fluid production well 106, and the pressure within the fluid production well 106.

The system 400 of FIG. 4 is similar to the system 100 of FIG. 1 except that, in the system 400 of FIG. 4, the fluid injection well 404 and the fluid production well 406 are angled. The wells 404, 406 extend from different locations on the earth's surface 114 and come together at a common bottom point 430 below the earth's surface 114. In the illustrated implementation, both angled boreholes 404, 406 extend into the underground hot dry rock formation 102 and the common bottom point 430 is within the underground hot dry rock formation 102. In other implementations, the common bottom point 430 is below the hot dry rock formation and each borehole 404, 406 passes through the hot dry rock formation 102.

A turbine-generator 108 is in the fluid injection well 404 and is arranged so as to convert kinetic energy of fluid flowing down through the fluid injection well 404 into electrical energy. Typically, such fluid flows down through the fluid injection well 104 at least partially under the influence of gravity and, in some implementations, flows entirely under the influence of gravity. Accordingly, the angle at which the fluid injection well 404 is disposed, may be critical in assuring that adequate fluid flow exists through the turbine-generator. An angle that is too shallow may reduce the kinetic energy of fluid flowing through the turbine-generator 108 to an unacceptable level.

The system 500 of FIG. 5 is similar to the system 400 of FIG. 4 except that, the system 500 of FIG. 5 includes a booster pump 532 coupled to pipe 120 and arranged to help move fluid from the heat exchanger 112 to the fluid injection well 404. In some instances, the booster pump 532 also helps urge fluid down the fluid injection well 404, which may be desirable because, such urging may, in certain implementations, increase the amount of kinetic energy in the fluid moving through the turbine-generator 108. If the fluid moving through the turbine-generator 108 has a greater amount of kinetic energy, then the turbine-generator may be able to produce a greater amount of electrical energy.

A booster pump, such as the booster pump 532 in the illustrated system 500, may be incorporated into any system where it is desirable, for example, to help move fluid to a fluid injection well or to urge fluid down the fluid injection well.

The system 600 of FIG. 6 is similar to the system 100 of FIG. 1 except that, the system 600 of FIG. 6 includes a home or industrial heating system 612 to extract absorbed heat from the heated fluid. In the illustrated implementation, heated fluid from the production well 106 is directed into and through the home or industrial heating system 612. The heated fluid releases heat into the home or industrial space that surrounds the heating system 612.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.

For example, a system may include multiple fluid injection wells and/or multiple fluid production wells. Moreover, the number of fluid injection wells and fluid production wells may not be identical. In such instances, multiple turbine-generators may be arranged to convert kinetic energy of fluid flowing through the various fluid injection wells, respectively. Additionally, multiple turbine-generators may be located at different heights in a single fluid injection well. Some systems may include one or more angled boreholes and one or more substantially vertical boreholes.

The heat extracted from the heated fluid for use in connection with a domestic or industrial application may be used to produce steam for a turbine-generator, to facilitate heating in some industrial application, or for any other useful application that uses heat.

Moreover, returning the primary fluid from the heat exchanger to the fluid injection port is optional. In some instances, fluid may not be recirculated back into the fluid introduction well after its heat is extracted for some useful purpose.

The boreholes and/or passages in or near the hot dry rock formation may be formed in any convenient shape or configuration. In general, the arrangement of boreholes and passages should provide fluid with the opportunity to absorb heat from an underground hot dry rock formation.

Any underground source of heat (e.g., hot dry rock, hot wet rock, etc.) may be suitable to provide heat to the fluid flowing through the wells and/or passages.

The design of the turbine-generator may vary as may the design of the pump(s) vary. The pump(s), for example, may be centrifugal pumps or positive displacement pumps. The system may include a variety of valve arrangements to help control the flow of fluid. The system also may include a control system adapted to control various aspects of the system's operation.

The fluid may be water or any other fluid that is suitable for a particular application. For example, in some instances, the fluid may have a relatively low boiling point. The pipes described herein could be any kind of conduit or channel adapted to carry fluid.

In certain instances, one or more of the wells may be configured such that they are not in direct physical contact with the hot rock formation.

The domestic or industrial applications in which the extracted heat may be utilized can vary greatly. Indeed, such applications can include the application of heated fluid to any useful purpose.

Accordingly, other implementations are within the scope of the following claims. 

1. A method comprising: introducing fluid to one or more underground fluid passages in thermal contact with a hot rock formation; converting kinetic energy of the fluid being introduced to the one or more underground fluid passages into electrical energy; absorbing heat from the hot rock formation into the introduced fluid; and extracting the absorbed heat from the heated fluid for use in connection with a domestic or industrial application.
 2. The method of claim 1 wherein the hot rock formation is an underground hot dry rock formation.
 3. The method of claim 1 wherein converting the kinetic energy of the fluid being introduced comprises directing the fluid through a turbine-generator.
 4. The method of claim 3 wherein the fluid flows through the turbine-generator at least partially under the influence of gravity.
 5. The method of claim 3 wherein the fluid flows through the turbine-generator entirely under the influence of gravity.
 6. The method of claim 3 wherein the turbine-generator is positioned as near as possible to the hot rock formation without undue risk that static fluid may accumulate above the hot rock formation to a level that will unduly impede fluid flow through the turbine-generator.
 7. The method of claim 1 further comprising: prior to extracting the absorbed heat from the heated fluid, removing the heated fluid from thermal contact with the hot rock formation.
 8. The method of claim 7 wherein the heated fluid is removed from thermal contact with the hot rock formation with a pump.
 9. The method of claim 7 wherein the heated fluid is a vapor that is removed from thermal contact with the hot rock formation by naturally flowing upward.
 10. The method of claim 1 wherein the fluid is introduced through a fluid injection well that extends from the earth's surface to the hot rock formation and wherein the fluid is removed through a fluid production well that extends from the earth's surface to the hot dry rock formation.
 11. The method of claim 10 wherein the one or more underground passages comprise a horizontal borehole in the hot rock formation, wherein the horizontal borehole extends between the fluid injection well and the fluid production well.
 12. The method of claim 10 wherein the one of more underground passages comprise a plurality of fractures formed in the hot rock formation, wherein the plurality of fractures extend between the fluid injection well and the fluid production well.
 13. The method of claim 1 wherein heat is extracted from the heated fluid for use in connection with a domestic or industrial application by a heat exchanger located above the hot rock formation.
 14. The method of claim 1 further comprising using the extracted heat in connection with a domestic or industrial application.
 15. The method of claim 1 further comprising: after extracting the absorbed heat from the heated fluid, returning the fluid to be reintroduced to the one or more underground fluid passages.
 16. A system comprising: an underground hot rock formation; a fluid injection well that facilitates introducing fluid to one or more underground fluid passages in thermal contact with the underground hot rock formation; and a turbine-generator arranged to convert kinetic energy of the fluid being introduced into electrical energy; wherein the system is arranged so that introduced fluid absorbs heat from the hot rock formation and wherein the absorbed heat is extracted for use in connection with a domestic or industrial application.
 17. The system of claim 16 wherein the hot rock formation is an underground hot dry rock formation.
 18. The system of claim 16 wherein the system is arranged so that fluid introduction occurs at least partially under the influence of gravity.
 19. The system of claim 16 wherein the system is arranged so that fluid introduction occurs entirely under the influence of gravity.
 20. The system of claim 16 wherein the turbine-generator is positioned as near as possible to the hot rock formation without undue risk that static fluid may accumulate above the hot rock formation to a level that will unduly impede fluid flow through the turbine-generator.
 21. The system of claim 16 further comprising a fluid production well to facilitate removing heated fluid from the one or more underground passages.
 22. The system of claim 21 further comprising a pump beneath a static fluid level in the fluid production well to remove fluid from thermal contact with the hot rock formation.
 23. The system of claim 21 arranged so that the heated fluid is a vapor that is removed from thermal contact with the hot rock formation by naturally flowing upward through the fluid production well.
 24. The system of claim 16 wherein the one or more underground passages comprise a horizontal borehole in the hot rock formation, wherein the horizontal borehole extends between the fluid injection well and a fluid production well arranged to facilitate removal of the heated fluid from the horizontal borehole.
 25. The system of claim 16 wherein the one of more underground passages comprise a plurality of fractures formed in the hot rock formation, wherein the fractures extend between the fluid injection well and a fluid production well arranged to facilitate removal of the heated fluid from the plurality of fractures.
 26. The system of claim 16 further comprising a heat exchanger to extract the absorbed heat from heated fluid for use in connection with a domestic or industrial application.
 27. The system of claim 26 further comprising: a pipe extending from the heat exchanger to the fluid injection well to return fluid, after the absorbed heat is extracted, to be reintroduced to the one or more underground fluid passages.
 28. A system comprising: an underground hot rock formation having one or more surfaces that define one or more underground fluid passages in thermal contact with a hot dry rock formation; a fluid injection well arranged to facilitate introducing fluid to the one or more underground fluid passages, wherein the introduced fluid absorbs heat from the hot rock formation; a fluid production well arranged to facilitate removing fluid from the one or more underground fluid passages; a turbine-generator arranged in the fluid introduction well to convert kinetic energy of the fluid being introduced into electrical energy; and a heat exchanger to extract the absorbed heat for use in connection with a domestic or industrial application. 